JP2024060106A - Plasma CVD equipment for diamond synthesis - Google Patents

Abstract

[Problem] Conventional diamond synthesis devices using microwave plasma CVD are roughly divided into cavity resonance type and non-cavity resonance type. The former are capable of generating high-density plasma and high-speed film formation, but the reaction vessel is spherical or a special flat dome shape, and the manufacturing cost is high, so reducing the manufacturing cost is an issue. The latter is slow in film formation, so high-speed film formation is an issue. To provide a diamond synthesis device capable of solving this problem. [Solution] The substrate placement stage, which is placed in a reaction vessel in which microwaves are supplied through a quartz window or antenna rod and plasma is generated, is arranged so that the electric field direction is perpendicular to the main surface of the substrate placement stage, and the main surface is provided with a plurality of grooves, holes, or protrusions. High-density plasma can be generated by concentrating the electric field due to the grooves, etc., and by selecting a frequency from 300 MHz to 3 GHz, diamond can be synthesized at high speed over a large area, and the manufacturing cost of the device can be reduced. [Selected Figure] Figure 4

Description

The present invention relates to a plasma CVD apparatus for synthesizing diamond. In particular, the present invention relates to a plasma CVD apparatus for synthesizing diamond in which the frequency of the plasma generating power source is in the microwave band.

Diamond is not only used for jewelry and machining materials, as described in Non-Patent Documents 1 and 2, but is also known as a wide-gap semiconductor and has properties far superior to semiconductors such as Si and SiC, and is therefore attracting attention as the ultimate power semiconductor material. In order to apply diamond to power semiconductor materials, intensive research and development is being conducted on large-area diamond formation equipment that can handle 4- to 5-inch-class substrates.
The method of forming diamond as a power semiconductor material is mainly microwave plasma CVD. The following is also known. That is, in the microwave plasma CVD method, when diamond is used as a substrate, diamond is formed by homoepitaxial growth, impurities can be easily controlled, and a crystal without distortion can be formed. In addition, when the substrate is other than diamond, diamond is formed by heteroepitaxial growth, which may cause distortion and reduce crystallinity.

The microwave plasma CVD method is characterized by using microwaves to heat the substrate and decompose the raw material gas. That is, by using microwaves to make the mixed gas of methane (CH ₄ ) and hydrogen (H ₂ ), which is the raw material gas, plasma, CH ₃ radicals and atomic hydrogen H, which are the main radicals indispensable for forming diamond film, are generated by electrons and ions generated in the plasma, and the substrate temperature required for promoting plasma chemical reaction on the substrate is heated to about 700°C to about 1.00°C by using the microwaves. The diamond formed on the substrate uses CH ₃ radicals as the main precursor, and is chemically adsorbed on the substrate, and hydrogen components and graphite components are eliminated by atomic H, etc. on the substrate, and diamond crystal grows. It is known that the growth rate of diamond crystal is generally about 1 to 10 μm/h.

Representative patent technologies relating to diamond synthesis apparatuses by microwave plasma CVD include diamond synthesis apparatuses by microwave plasma CVD using an antenna electrode, such as those described in Patent Documents 1 to 4.
Patent Document 1 describes a vacuum chamber made of a conductive material, a first antenna fixed to an upper wall surface inside the vacuum chamber, having a through hole, and made of a conductive material, and a stage arranged opposite the first antenna and capable of mounting a substrate, one end of the through hole being connected to the outside of the vacuum chamber and the other end of the through hole being located on a surface of the first antenna facing the stage, raw material gas for plasma is supplied from the one end of the through hole through the other end to a gap between the first antenna and the stage, and a first space formed between an outer wall of the stage and an inner wall of the vacuum chamber or a second space formed between the outer side of the first antenna and the stage is supplied with a plasma. a second space formed between the wall and the inner wall of the vacuum chamber as a waveguide, microwaves are supplied from outside the vacuum chamber via a route different from that of the raw material gas, plasma is generated in the gap between the first antenna and the stage, the distance between the first antenna and the stage is 1/10 or less of the free space wavelength of the microwaves, and the outer diameter of the first antenna is equal to or more than half the free space wavelength of the microwaves, and the surface of a substrate mounted on the stage can be observed through the through hole.
Patent Document 2 discloses a microwave plasma CVD apparatus having at least a vacuum chamber having an opening for introducing microwaves, a waveguide for guiding microwaves to the opening, a dielectric window for introducing microwaves into the vacuum chamber, an antenna section having an electrode section formed at an end for introducing microwaves into the vacuum chamber, and a substrate support stand for supporting a substrate within the vacuum chamber, the dielectric window being sandwiched between the inner surface of the vacuum chamber and the electrode section, the end face of the electrode section being formed wider than the end face of the dielectric window so as to conceal the dielectric window, and a recess being formed in the center of a surface of the electrode section facing the center of the vacuum chamber, the width across the surface of the recess facing the center of the vacuum chamber being within the range of 1/3 to 5/3 of the wavelength of the microwaves to be introduced, and the depth from the surface facing the center of the vacuum chamber to the deepest part of the recess being within the range of 1/20 to 3/5 of the wavelength of the microwaves to be used.

Patent Document 3 discloses a CVD apparatus for diamond synthesis that forms a thin film of single crystal diamond on the surface of a diamond substrate, the CVD apparatus comprising a spherically shaped discharge chamber, a coaxial antenna that supplies microwaves into the interior of the discharge chamber, and a mounting member provided at the tip of the coaxial antenna, the mounting member or the diamond substrate placed on the mounting member being positioned at the center of the discharge chamber, microwaves radiated from the mounting member being reflected by the inner surface of the discharge chamber and returning to the center of the discharge chamber, and the amplitude of the microwaves being maximum at the center of the discharge chamber.
Patent Document 4 discloses a CVD apparatus for diamond synthesis for forming a diamond film on the surface of a substrate, the CVD apparatus comprising: a discharge chamber composed of an upper hemisphere having a flat dome shape and a lower hemisphere having a flat dome shape; a coaxial antenna member extending along the central axis of the discharge chamber, penetrating the lower hemisphere, and supplying microwaves to the inside of the discharge chamber; a disk-shaped resonant antenna attached to the tip of the coaxial antenna member within the discharge chamber, and extending concentrically with the central axis along the maximum diameter surface of the discharge chamber; and a mounting table on which the substrate is placed, having a circular outer periphery and positioned concentrically with the central axis at the center of the upper surface of the resonant antenna.

Patent 5071927 Patent 5142074 Patent 4649153 Patent 7304280

Osamu Ariyada, CVD Apparatus for Diamond Synthesis, Vacuum Journal, January 2023, 24-26 Hideaki Yamada, Current status and challenges of single crystal diamond synthesis by plasma CVD, J. Plasma Fusion Res. Vol.90, No.2 (2014) 152-158 Noboru Yoshikawa, Fundamentals and Applications of Microwave Heating of Metals, Materia Japan, Vol. 48 (2009), No. 1, 3-10

Conventional diamond synthesis apparatus using microwave plasma CVD can be broadly divided into cavity resonance types in which high-density plasma is generated by the supplied microwave power being reflected inside the reaction vessel and causing cavity resonance, and non-cavity resonance types in which the cavity resonance does not occur.
The devices described in Patent Documents 1 and 2 are not only disadvantageous in that they are non-cavity resonant types and have low plasma density, but also have a problem in that the propagation direction of the supplied microwave power turns at a right angle at one point in the microwave introduction propagation path that introduces the microwave power into the reaction vessel, which causes a large power loss, making it difficult to generate high density plasma. As a result, it is difficult to increase the diamond synthesis speed.
The devices described in Patent Documents 3 and 4 are of a cavity resonance type, and employ a coaxial antenna electrode that suppresses power loss in the microwave power introduction propagation path. Since the loss in the microwave introduction propagation path is small, it can be said that these devices are suitable for diamond synthesis.
However, the device described in Patent Document 3 has a problem that the manufacturing of the plasma reaction chamber is difficult and the manufacturing cost is high because a spherical chamber is used, whereas the device described in Patent Document 4 has a problem that the manufacturing of the plasma reaction chamber is difficult and the manufacturing cost is high because the shape of the plasma reaction chamber is a hemisphere having a flat dome shape.
That is, the devices described in Patent Documents 1 and 2 have a problem of improving plasma density, while the devices described in Patent Documents 3 and 4 have a problem of reducing manufacturing costs.
An object of the present invention is to provide a plasma CVD apparatus for synthesizing diamond using a power frequency in the microwave band, which is capable of solving the problems associated with the above-mentioned conventional apparatus.

A first aspect of the present invention for solving the above-mentioned problems is a plasma CVD apparatus for diamond synthesis comprising a reaction vessel having a source gas introduction means for introducing a source gas, an exhaust means, and a substrate mounting table on which a substrate is mounted, and a microwave power supply device for supplying microwaves to the reaction vessel through a dielectric window or an antenna rod, the source gas introduced from the source gas introduction means being converted into plasma by the microwaves supplied from the microwave power supply device, thereby forming diamond on a surface of the substrate mounted on the substrate mounting table,
The substrate supporting table has a main surface in contact with the substrate, the main surface is arranged parallel to a plane perpendicular to the electric field direction of the microwaves supplied from the microwave power supply device, and a plurality of grooves, a plurality of holes, or a plurality of protrusions are formed on the main surface.
A second invention is characterized in that, in the first invention, the plurality of grooves on the main surface of the substrate mounting table have a rectangular cross-sectional shape and are arranged concentrically with a central axis of the substrate mounting table.
A third invention is characterized in that, in the first invention, the multiple holes in the main surface of the substrate supporting table have a rectangular cross-sectional shape, and the centers of adjacent multiple holes are arranged at approximately equal intervals.
A fourth invention is characterized in that, in the first invention, the multiple protrusions on the main surface of the substrate supporting table have a cross-sectional shape that is triangular or sinusoidal, and are arranged concentrically with a central axis of the substrate supporting table.
A fifth invention is any one of the first to fourth inventions, characterized in that the microwave power supply device generates microwave power of a frequency selected from the range of 300 MHz to 3 GHz.

In the CVD apparatus for diamond synthesis of the present invention, the substrate mounting table, which is an apparatus component, has a main surface that contacts the substrate, the main surface is arranged parallel to a plane perpendicular to the electric field direction of the microwave supplied from the microwave power supply device, and a plurality of grooves, holes, or protrusions are formed on the main surface, so that high-density plasma can be generated near the substrate surface by the electric field concentration effect of the grooves, holes, or protrusions.The generation of high-density plasma has the effect of accelerating the growth rate of diamond.
Since the uniformity of the plasma depends on the electric field distribution of the standing wave generated in the reaction vessel, a low microwave frequency is selected for large area substrates, for example, 300 MHz, and a high microwave frequency is selected for small area substrates, for example, 915 MHz.
This enables high-quality diamond synthesis at high speed over a large area, and has the effect of solving the above problems. The simple structure of the reaction vessel allows the manufacturing cost of the device to be reduced. In other words, the effects of solving the problems of conventional devices are achieved.

FIG. 1 is a schematic cross-sectional view showing the configuration of a plasma CVD apparatus for synthesizing diamond according to a first embodiment of the present invention. FIG. 2 is a conceptual diagram of a standing wave of microwaves generated in a reaction vessel which is a component of the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view of a reaction vessel which is a component of a plasma CVD apparatus for synthesizing diamond according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view showing the configuration of a first substrate placement table and source gas introduction means which are components of a plasma CVD apparatus for diamond synthesis according to a first embodiment of the present invention. FIG. 5 is a schematic perspective view showing a plurality of holes provided in a first substrate mounting table which is a component of a plasma CVD apparatus for diamond synthesis according to a first embodiment of the present invention. FIG. 6 is a schematic cross-sectional view showing the electric field concentration effect of a plurality of holes formed in the surface of a first substrate mounting table which is a component of a plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. FIG. 7 is a schematic conceptual diagram of a high-density plasma generated in the vicinity of a substrate placed on a first substrate mounting table having a plurality of holes, which is a component of a plasma CVD apparatus for diamond synthesis according to a first embodiment of the present invention. FIG. 8 is a schematic diagram showing the principle of diamond formation by plasmatization of a raw material gas (a mixed gas of methane _CH4 and hydrogen _H2 ) in a plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. FIG. 9 is a schematic cross-sectional view showing the configuration of a plasma CVD apparatus for synthesizing diamond according to the second embodiment of the present invention. FIG. 10 is a schematic cross-sectional view of a second substrate placement table which is a component of a plasma CVD apparatus for diamond synthesis according to a second embodiment of the present invention. FIG. 11 is a cross-sectional view showing the structure of a third substrate mounting table which is a component of a plasma CVD apparatus for diamond synthesis according to the third embodiment of the present invention. FIG. 12 is a cross-sectional view showing the structure of a fourth substrate mounting table which is a component of a plasma CVD apparatus for diamond synthesis according to the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicated explanations will be omitted.
The present invention is not limited to the following description, and can be modified as appropriate without departing from the scope of the present invention. In addition, for the convenience of explanation, the scale of each component in the drawings shown below may differ from the actual scale. In addition, the scale of each drawing may differ from the actual scale.

First Embodiment
First, the configuration of a plasma CVD apparatus for synthesizing diamond according to a first embodiment of the present invention will be described with reference to FIGS.
Fig. 1 is a schematic cross-sectional view showing the configuration of a plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. Fig. 2 is a conceptual diagram of a standing wave of microwaves generated in a reaction vessel which is a component of the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. Fig. 3 is a cross-sectional view of a reaction vessel which is a component of the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. Fig. 4 is a cross-sectional view showing the configuration of a first substrate mounting table and a raw material gas introduction means which are components of the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. Fig. 5 is a schematic perspective view showing a plurality of holes provided in a first substrate mounting table which is a component of the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. Fig. 6 is a schematic cross-sectional view showing the electric field concentration effect of a plurality of holes formed on the surface of a first substrate mounting table which is a component of the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. FIG. 7 is a schematic conceptual diagram of a high-density plasma generated in the vicinity of a substrate placed on a first substrate mounting table having a plurality of holes, which is a component of a plasma CVD apparatus for diamond synthesis according to a first embodiment of the present invention.

As shown in FIG. 1, the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention comprises a reaction vessel 7 equipped with a raw material gas introduction means 13 for introducing raw material gas, an exhaust means having exhaust ports 15a, 15b, and a first substrate mounting table 12 on which a substrate 11 is placed, and a first microwave power supply unit 1 for supplying microwave power to the reaction vessel 7 via a waveguide 2 and a dielectric window 5.
As shown in FIG. 1, the first microwave power supply device 1 includes a waveguide 2 for propagating microwaves, a first microwave generator (e.g., a magnetron) 1a provided at one end of the waveguide 2 for generating microwaves, a matching device 3c attached to the waveguide 2 for performing load impedance matching for adjusting the reflected wave of the microwave, an isolator 3a attached between the first microwave generator 1a and the matching device 3c for absorbing the reflected wave returning inside the waveguide, and a power monitor 3b provided between the isolator 3a and the matching device 3c.
As shown in Fig. 3, the reaction vessel 7 has a rectangular cross-sectional shape consisting of a long side a and a short side b, and constitutes a cavity resonator having a length L for cavity resonance of electromagnetic waves. That is, as shown in Figs. 1 to 4, the reaction vessel 7 has a rectangular parallelepiped structure in which the long side a of the rectangle is the top surface 7a and the bottom surface 7b, the short side b of the rectangle is the first side surface 7c and the second side surface 7d, the end surface on the waveguide 2 side of the end surface in the length L direction for cavity resonance is the first end surface 7e, and the other end surface is the second end surface 7f.
The structure of the reaction vessel 7 is not limited to a rectangular parallelepiped, and may be a cylindrical or double-ridge type, as long as it is an electromagnetic wave cavity resonator.
The first end surface 7e is opened, and a dielectric window 5 (e.g., a quartz window) that transmits microwave power supplied from the waveguide 2 of the microwave power supply device 1 to the reaction vessel 7 is disposed thereon. A vacuum seal is provided at the joint between the waveguide 2, the dielectric window 5, and the first end surface 7e of the reaction vessel 7 to prevent vacuum leakage.
A plunger 9 used for adjusting the phase of the microwave power supplied from the microwave power supply device 1 to the reaction vessel 7 is disposed on the second end surface 7 f.
The first microwave power supply device 1 is capable of generating and transmitting electric power at a frequency selected from the microwave band of 300 MHz to 3 GHz.
The reason why the power supply frequency is selected from the microwave band of 300 MHz to 3 GHz is that the effects of dielectric heating, magnetic heating, and induction heating by high-frequency power are large in this frequency band, so that the means for generating plasma and the means for heating the substrate can be used together. In addition, the power supply of 300 MHz to 500 MHz has the advantage that it can be manufactured inexpensively by combining a quartz oscillator and a power amplifier, and the power supplies of frequencies of 915 MHz and 2,450 MHz have the advantage that commercially available products can be used as magnetron power supplies. It is known that dielectric heating is proportional to ε·E ² (where ε is the dielectric constant, E is the strength of the electric field), magnetic heating is proportional to μ·H ² (where μ is the magnetic permeability, H is the strength of the magnetic field), and induction heating is proportional to σ·E ² (where σ is the electrical conductivity, E is the strength of the electric field).
Here, as the first microwave generating device 1a, for example, a magnetron device that generates microwaves of 915 MHz is used.

A first substrate mounting table 12 (described later) is provided on the bottom surface 7b in the center of the reaction vessel 7. A raw material gas ejection box 13 including a raw material gas introduction pipe 13a, a raw material gas dispersion cavity 13b, and raw material gas ejection holes 13c is provided on the top surface 7a in the center of the reaction vessel 7 facing the first substrate mounting table 12.
The raw material gas ejection holes 13c are formed of a large number of holes having a diameter of 0.1 to 1.0 mm, and the raw material gas ejected from the raw material gas ejection holes 13c is uniformly dispersed inside the reaction vessel 7.
An inlet/outlet 26a for the substrate 11 is disposed on a second side surface 7d of the reaction vessel 7. The substrate inlet/outlet passage opening 26a is used for loading and unloading the substrate 11 via a substrate inlet/outlet passage 26 and a substrate inlet/outlet valve 27. The substrate inlet/outlet valve 27 is connected to, for example, a load lock chamber (not shown).
An observation window 19 is disposed on the top surface 7a of the reaction vessel 7, through which the state inside the reaction vessel can be observed and the surface temperature of the substrate 11 can be measured by a radiation thermometer.
The dimensions of the reaction vessel 7 are selected according to the size of the target substrate 11. For example, if the substrate size 11 is 5 inches in diameter, the long side a is, for example, 248 mm, the short side b is, for example, 124 mm, and the length L is, for example, 490 mm.
The dimensions of the reaction vessel 7 are not limited to the above example, and a predetermined value is selected taking into consideration the wavelength of the microwaves to be used.
Aluminum (Al) or SUS is used as the material for the reaction vessel 7. A cooling pipe (not shown) is installed in the reaction vessel 7 so that the temperature of the reaction vessel 7 does not become too high.

By operating exhaust ports 15a and 15b in combination with a vacuum pump (not shown), it is possible to adjust the pressure inside reaction vessel 7 to a predetermined value and maintain the pressure at a predetermined value. It is also possible to evacuate the inside of reaction vessel 7 to a high degree of vacuum. The installation position of exhaust ports 15a and 15b is not limited to the bottom surface 7b of reaction vessel 7, and they may be located, for example, on the top surface 7a.

The first substrate mounting table 12 is disposed on the bottom surface 7b in the center of the reaction vessel 7. As shown in Figs. 4 and 5, the first substrate mounting table 12 has a main surface 12a in contact with the substrate 11, the main surface 12a is disposed parallel to a plane perpendicular to the electric field direction of the microwave supplied from the first microwave power supply device, and a plurality of holes 12b (holes with a bottom) are formed in the main surface 12a. That is, the main surface is disposed in a direction parallel to the bottom surface 7b. By aligning the normal direction of the main surface 12a of the first substrate mounting table 12 with the electric field direction of the microwave, it is possible to concentrate electric field lines due to the edge effect of the plurality of holes 12b.
The holes 12b have edges having an electric field concentration effect as described below, and have a diameter of 0.5 mm to 10 mm, for example 3 mm, and a depth of 1.0 mm to 10 mm, for example 5 mm. The interval between adjacent holes 12b is 1 mm to 10 mm, for example 3 mm, between the edges of the holes.
The material of the first substrate support table 12 is made of molybdenum (Mo), chromium (Cr), or titanium (Ti), because molybdenum (Mo), chromium (Cr), or titanium (Ti) is paramagnetic and conductive, has a high heating effect when heated by microwaves, is easily heated to high temperatures when electromagnetic waves are applied, and has a high melting point and excellent mechanical strength.
It is known that, as described in Non-Patent Document 3, for example, when heating metals and dielectrics with microwaves, dielectric heating is proportional to ε· ^E2 (where ε is dielectric constant and E is electric field strength), magnetic heating is proportional to μ· ^H2 (where μ is magnetic permeability and H is magnetic field strength), and induction heating is proportional to σ· ^E2 (where σ is electrical conductivity and E is electric field strength). In other words, materials with high dielectric constant, magnetic permeability and electrical conductivity have a large heating effect and are heated effectively. Among these, molybdenum (Mo), which has the highest melting point, is preferred.
The shape of the main surface 12a of the first substrate mounting table 12 is similar to the shape of the substrate. When the substrate 11 is circular, the shape of the main surface 12a of the first substrate mounting table 12 is circular. When the substrate 11 is rectangular, the shape of the main surface 12a of the first substrate mounting table 12 is rectangular. Here, it is assumed to be circular. The size is one size larger than the size of the substrate 11, and for example, in the case of a substrate with a diameter of 5 inches, the diameter is, for example, 137 mm. Note that the first substrate mounting table 12 may include a frame 12c that is concentric with the central axis 21 of the substrate mounting table 12 and has a diameter approximately 0.5 mm larger than the size of the substrate, in order to ensure stability in holding the substrate, or may include a pin for positioning the substrate.
The first substrate mounting table 12 includes a cooling unit 12d (not shown) inside the first substrate mounting table 12. The cooling unit 12d is cooled by a cooling medium (not shown) supplied from the outside of the reaction vessel 7.
Here, the substrate 11 is, for example, a single crystal Si wafer coated with an iridium crystal film having a diameter of 5 inches. Note that the substrate 11 is not limited to a single crystal Si wafer, and for example, a plurality of small diamond substrates manufactured by a high-temperature, high-pressure method may be placed on the substrate.
The substrate 11 is loaded and unloaded from a loading/unloading port 26a disposed on the second side surface 7d of the reaction vessel 7 via a substrate loading/unloading passage 26 and a substrate loading/unloading valve 27. The substrate loading/unloading valve 27 is connected to, for example, a load lock chamber (not shown).
The substrate 11 itself is heated by microwave power, and is also heated by thermal radiation and thermal conduction from the first substrate mounting table 12. The temperature of the substrate 11 is set to about 700 to about 1,200° C., for example, 1,000° C. The temperature of the substrate 11 is measured by a radiation thermometer 19 through an observation window 19.

The distance d between the main surface 12a of the first substrate mounting table 12 and the surface of the raw material gas introduction means 13 facing the substrate mounting table 12 is an important parameter when generating the plasma 22 described below. That is, the optimal electric field (output of the first microwave power supply device 1) for plasma generation follows the pd curve of Paschen's law, which is expressed as the product pd of the pressure p inside the reaction vessel 7 and the distance d, and therefore the pressure p and the distance d are determined by adjusting both. Here, the distance d is, for example, in the range of 3 mm to 20 mm, and is set to 5 mm.

Microwave power is supplied from the first microwave power supply device 1 to the reaction vessel 7 through the dielectric window 5, and the plunger 9 and the matching box 3c are adjusted. Then, a standing wave 25 as shown in Fig. 2 is generated. That is, as shown in Fig. 3, an electric field 25a is generated in the region between the first substrate mounting table 12 and the raw material gas injection box 13. If the electric field 25a satisfies the plasma generation condition determined by Paschen's law, a plasma 22 is generated in the plasma generation region 23 as shown in Fig. 4.
When the electric field 25a is generated, as shown by electric field lines 12ba in Fig. 6, an electric field concentration 12bb is generated due to the edge effect of the multiple holes 12b provided in the main surface 12a of the first substrate mounting table 12. When the electric field concentration 12bb is generated, a high-density plasma 22a is generated in an electric field concentration region 12bf in the vicinity of the electric field concentration 12bb, as shown in Fig. 6.
When the substrate 11 is placed on the first substrate mounting table 12, if the material of the substrate 11 is a dielectric material, such as a silicon wafer or a diamond substrate, the shape of the electric field lines 12ba will be similar to the electric field lines 12ba shown in FIG. 6, and high-density plasma 22a will be generated in the electric field concentration region 12bf, as shown in FIG. 7.
That is, the electric field 25a generates a plasma 22 with a high density plasma 22a in the plasma generation region 23 shown in FIG.

2, the standing wave 25 generated in the region between the first substrate mounting table 12 and the raw material gas ejection box 13 has a cosine wave shape in the direction of the length L of the reaction vessel 7, and therefore the region in which uniform plasma is generated is a range of a diameter of approximately 0.25λ centered on the central axis 21 of the first substrate mounting table 12. Therefore, for example, when the power supply frequency is 2.45 GHz, the range of uniform plasma is 0.75×0.25×122 mm=22.8 mm, assuming that the wavelength shortening rate in the plasma is 0.75 and λ=122 mm.
For example, when the power supply frequency is 915 MHz, the range of the uniform plasma is 0.75×0.25×122 mm=61.1 mm, assuming that the wavelength shortening rate in the plasma is 0.75 and λ=326 mm.
For example, when the power supply frequency is 300 MHz, the range of the uniform plasma is 0.75×0.25×996 mm=186.7 mm, assuming that the wavelength shortening rate in the plasma is 0.75 and λ=996 mm.
Therefore, when the area of the substrate is large, the frequency of the supplied power is set low, for example, in the band of 300 MHz to 600 MHz, and when the area of the substrate is small, the frequency of the supplied power is set high, for example, to 915 MHz or 2.45 GHz, thereby enabling uniform diamond synthesis through the generation of uniform plasma.

Next, the operation procedure of the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention will be described with reference to Fig. 1 to Fig. 8. Fig. 8 is a schematic diagram showing the principle of diamond formation by plasmatization of raw material gas (mixture of methane _CH4 and hydrogen _H2 ) in the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention.
First, the inside of the reaction vessel 7 is evacuated to a predetermined vacuum level through the exhaust ports 15a and 15b by a vacuum pump (not shown).
Next, the substrate 11 is loaded from the substrate loading/unloading passage opening 26a through the substrate loading/unloading passage opening 26 and the substrate loading/unloading valve 27, and placed on the first substrate placement table 12. The upstream side of the substrate loading/unloading valve 27 is connected to a load lock chamber (not shown) and is kept under vacuum.
Next, the surface of the substrate 11 is cleaned with hydrogen plasma, and the temperature of the substrate is set to, for example, 1,000° C. That is, only hydrogen gas is introduced as the raw material gas from a raw material gas supply source (not shown), and the pressure inside the reaction vessel 7 is set to, for example, 5 kPa. Then, for example, 1 kW is supplied from the first microwave power supply device 1 to the reaction vessel 7. At this time, the matching conditions for microwave propagation are adjusted by the isolator 3a, power monitor 3b (traveling wave, reflected wave), matching device 3c, and plunger 9 attached to the waveguide 2. The surface temperature of the substrate 11 is measured through the observation window 19 using a radiation thermometer (not shown), and when it reaches, for example, 1,000° C., the output of the first microwave power supply device 1 is temporarily reduced to zero. The substrate 11 and the first substrate support 12 are effectively heated by the magnetic heating effect (μ· ^H2 , where μ is magnetic permeability and H is magnetic field strength), the induction heating effect (σ· ^E2 , where σ is electrical conductivity and E is electric field strength) and the induction heating effect (σ· ^E2 , where σ is electrical conductivity and E is electric field strength).
Next, methane gas and hydrogen are selected as raw material gases from a raw material gas supply source (not shown). The gas supply conditions are, for example, a flow rate ratio of hydrogen flow rate/methane gas flow rate=100/1. Thereafter, methane gas and hydrogen gas, which are controlled to predetermined flow rates by mass flow controllers for methane gas and hydrogen gas (not shown) from a methane gas source (not shown) and a hydrogen gas source (not shown), are ejected from the raw material gas supply hole 13c.
Next, an exhaust valve control device (not shown) attached to the exhaust ports 15a and 15b controls the opening and closing of the exhaust valve (not shown) to keep the internal pressure of the dome-shaped reaction vessel 7 at about 1 kPa to about 10 kPa. Here, for example, the pressure is set to 5 kPa and maintained.

Next, the output of the first microwave generator 1a is set to, for example, 500 W to 2 kW, for example, 1 kW here. At this time, matching conditions for microwave propagation are adjusted using the isolator 3a, power monitor 3b (forward wave, reflected wave), matching box 3c, and plunger 9 attached to the waveguide 2. The surface temperature of the substrate 11 is measured through the observation window 19 using a radiation thermometer (not shown), and it is confirmed that it is, for example, 1,000°C.
Then, as shown in Fig. 4 and Fig. 7, plasma 22 accompanied by high density plasma 22a is generated in the region 23 (plasma generation region 23) between the first substrate mounting table 12 and the raw material gas introduction means 13. Since the plasma 22 is accompanied by the high density plasma 22a shown in Fig. 7, the raw material gas can be effectively decomposed near the surface of the substrate 11. When the raw material gas methane ( _CH4 ) and hydrogen ( _H2 ) are plasmatized by the high density plasma 22a, _CH4 and _H2 are dissociated, generating high concentration _CH3 radicals and atomic H, etc., which are precursors for diamond formation. The _CH3 radicals and the atomic H, etc. diffuse and reach the surface of the substrate 11.
That is, as shown in Fig. 8, the high concentration of _CH3 radicals and atomic H etc. generated in the plasma generation region 23 move to the surface of the substrate 11 by the diffusion phenomenon. A part of them is chemically adsorbed on the surface of the substrate 11. A part of the _CH3 radicals etc. chemically adsorbed on the substrate surface bonds in the form of C-C by a surface chemical reaction. The atomic H extracts H components and weakly bonded carbon components on the film surface and in the film. The extracted C and H components become gas and are discharged. On the substrate, C-C bonds are formed in a regular tetrahedral structure and diamond grows.

Next, since the thickness of the diamond formed is proportional to the duration of the generation of the plasma 22, the output of the first microwave power supply device 1 is set to zero when a predetermined time has elapsed since the start of output supply from the first microwave power supply device 1. The diamond synthesis time is determined based on previously acquired data. Here, for example, it is set to 30 to 60 minutes, for example, 60 minutes.
The diamond synthesis time is determined based on data relating to the diamond synthesis rate, such as the dimensions of the reaction vessel 7, the distance d between the first substrate mounting table 12 and the raw material gas introduction means 13, the substrate temperature, the flow rate of methane gas, the flow rate of hydrogen gas, pressure, microwave power, etc., which are previously obtained.
After the synthesis of the desired diamond is completed, the supply of the methane gas and hydrogen gas is stopped, and the inside of the reaction vessel 7 is temporarily evacuated to a high degree of vacuum.
Thereafter, the substrate 11 is carried out from the substrate carry-in/out passage opening 26a through the substrate carry-in/out passage 26 and the substrate carry-in/out valve 27. After the substrate 11 is carried out, a new substrate 11 is carried in. Then, diamond is formed in the same manner as described above.

As explained above, in the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention, a plurality of holes 12b are formed in the main surface 12a of the first substrate mounting table 12 placed in the reaction vessel 7, which contacts the substrate 11, and high-density plasma 22a can be generated in the vicinity of the main surface 12a due to the electric field concentration effect of the edges of the plurality of holes 12b. Since the range of uniform plasma in the plasma generation region 23 depends on the electric field distribution of the standing wave 25 generated inside the reaction vessel 7, it is possible to increase the area by selecting the frequency of the power generated by the first microwave power supply device 1.
For example, when the power supply frequency is 2.45 GHz, the range of the uniform plasma is 0.75×0.25λ=22.8 mm, assuming that the wavelength shortening rate in the plasma is 0.75 and λ=122 mm.
For example, when the power supply frequency is 915 MHz, the range of the uniform plasma is 0.75×0.25λ=61.1 mm, assuming that the wavelength shortening rate in the plasma is 0.75 and λ=326 mm.
For example, when the power supply frequency is 300 MHz, the uniform plasma has a wavelength shortening rate of 0.75 and a wavelength shortening rate of λ=996 mm, and the length is 0.75×0.25λ=186.7 mm.
Therefore, when the area of the substrate is large, the frequency of the power supply is set low, for example, in the band of 300 MHz to 600 MHz, and when the area of the substrate is small, the frequency of the power supply is set high, for example, to 915 MHz or 2.45 GHz, thereby enabling high-speed, large-area, and high-quality diamond growth. In addition, the structure of the reaction vessel is simple, and the reaction vessel is easy to manufacture, resulting in an effect of reducing the manufacturing cost.

Second Embodiment
The configuration of a plasma CVD apparatus for synthesizing diamond according to a second embodiment of the present invention will be described with reference to Figures 9 and 10. Figure 4 will also be referred to.
Fig. 9 is a schematic cross-sectional view showing the configuration of a plasma CVD apparatus for diamond synthesis according to the second embodiment of the present invention. Fig. 10 is a schematic cross-sectional view of a second substrate placement table which is a component of the plasma CVD apparatus for diamond synthesis according to the second embodiment of the present invention.
As shown in FIG. 9, the plasma CVD apparatus for diamond synthesis according to the second embodiment of the present invention comprises a reaction vessel 7 equipped with a raw material gas introduction means 13 for introducing raw material gas, an exhaust means having exhaust ports 15a, 15b, and a second substrate mounting table 16 on which a substrate 11 is placed, and a second microwave power supply device 50 for supplying microwave power to the reaction vessel 7 via an antenna rod 51.
As shown in FIG. 9, the second microwave power supply device 50 includes a coaxial tube 50b that propagates microwaves, a second microwave generator (e.g., a magnetron) 50a that is provided at one end of the coaxial tube 50b and generates microwaves, a matching device 50e that is attached to the coaxial tube 50b and performs load impedance matching to adjust the reflected wave of the microwave, an isolator 50c that is attached between the second microwave generator 50a and the matching device 50e and absorbs the reflected wave returning through the coaxial tube 50b, and a power monitor 50d that is provided between the isolator 50c and the matching device 50e.
As shown in Fig. 9, the reaction vessel 7 has a rectangular parallelepiped structure consisting of a top surface 7a, a bottom surface 7b, a first side surface 7c, a second side surface 7d, a first end surface 7e, and a second end surface 7f, similar to the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. Note that the structure of the reaction vessel 7 is not limited to a rectangular parallelepiped, and may be cylindrical or double-ridged.
Here, as shown in Fig. 9, the first end surface 7e is a wall. An antenna rod 51 is disposed near the first end surface 7e. The antenna rod 51 is connected to a matching box 50e via a coaxial pipe joint 51a and a coaxial pipe 50b. The antenna rod 51 radiates microwaves supplied from the second microwave power supply device 50. Note that a member for a vacuum device is used between the coaxial pipe 50b and the coaxial pipe joint 51a to prevent vacuum leakage.
A plunger 9 used for adjusting the phase of the microwave power supplied from the second microwave power supply device 50 to the reaction vessel 7 is disposed on the second end surface 7 f.
The second microwave power supply 50a is capable of generating power at a frequency selected from the microwave band of 300 MHz to 3 GHz.
The reason for selecting the power supply frequency from the microwave band of 300 MHz to 3 GHz is the same as in the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention.
Here, as the second microwave generating device 50a, for example, a magnetron device that generates microwaves of 915 MHz is used.

9 and 10, reference numeral 16 denotes a second substrate mounting table. The second substrate mounting table 16 is disposed on the bottom surface 7b in the center of the reaction vessel 7. As shown in Fig. 10, the second substrate mounting table 16 includes grooves 16b having a rectangular cross-sectional shape formed on a main surface 16a that contacts the substrate 11. The grooves 16b are a plurality of circular grooves that are concentric with a center line 21a of the second substrate mounting table 16.
The main surface 16a of the second substrate mounting table 16 is disposed parallel to a plane perpendicular to the electric field direction of the microwaves, that is, parallel to the bottom surface 7b of the reaction vessel 7.
The groove width of the plurality of grooves 16b is, for example, 0.5 mm to 10 mm, for example, 2 mm, the depth of the grooves 16b is, for example, 0.5 mm to 10 mm, for example, 5 mm, and the interval between the edges of adjacent grooves 16b is, for example, 1 mm to 10 mm, for example, 3 mm.
The material of the second substrate support table 16 is molybdenum (Mo), chromium (Cr) or titanium (Ti), for the same reason as in the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention.
The shape of the main surface 16a of the second substrate mounting table 16 is similar to the shape of the substrate. When the substrate 11 is circular, the shape of the main surface 16a of the second substrate mounting table 16 is circular. When the substrate 11 is rectangular, the shape of the main surface 16a of the second substrate mounting table 16 is rectangular. Here, it is assumed to be circular. The size is one size larger than the size of the substrate 11, and for example, in the case of a substrate with a diameter of 5 inches, the diameter is, for example, 137 mm. Note that, in order to ensure stability in holding the substrate, the main surface 16a of the second substrate mounting table 16 may be provided with a frame 16c that is concentric with the central axis 21a of the second substrate mounting table 16 and has a diameter that is approximately 0.5 mm larger than the size of the substrate, or may be provided with a pin (not shown) for substrate positioning.
The second substrate mounting table 16 includes a cooling unit 16d (not shown) inside the second substrate mounting table 16. The cooling unit 16d is cooled by a cooling medium (not shown) supplied from the outside of the reaction vessel 7.
Here, the substrate 11 is, for example, a single crystal Si wafer coated with an iridium crystal film having a diameter of 5 inches. Note that the substrate 11 is not limited to a single crystal Si wafer, and for example, a plurality of small diamond substrates manufactured by a high-temperature, high-pressure method may be placed on the substrate.
As in the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention, the substrate 11 is loaded and unloaded from a loading/unloading port 26a disposed on the second side surface 7d of the reaction vessel 7, via a substrate loading/unloading passage 26 and a substrate loading/unloading valve 27, as shown in Fig. 4. The substrate loading/unloading valve 27 is connected to, for example, a load lock chamber (not shown).
The substrate 11 itself is heated by microwave power, and is also heated by thermal radiation and thermal conduction from the second substrate mounting table 16. The temperature of the substrate 11 is set to about 700 to about 1,200° C., for example, 1,000° C. The temperature of the substrate 11 is measured through an observation window 19 using a radiation thermometer (not shown).
The distance d between the main surface 16a of the second substrate stage 16 and the surface of the source gas introduction means 13 facing the second substrate stage 16 is an important parameter in generating plasma, which will be described later. That is, since the optimal electric field (output of the microwave power supply device 2) in generating plasma follows a pd curve according to Paschen's law, which is expressed by the product pd of the pressure p inside the reaction vessel 7 and the distance d, the pressure p and the distance d are determined by adjusting both. Here, the distance d is, for example, in the range of 3 mm to 20 mm, and is set to 5 mm.

When microwaves are supplied from the second microwave generator 50a to the antenna rod 51 through the coaxial tube 50b, the microwaves are radiated from the antenna rod 51. The microwaves radiated from the antenna rod 51 propagate through the inside of the reaction vessel 7 and resonate therein, generating a standing wave 25, as in the case of the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention. The standing wave 25 generates an electric field 25a in the region between the main surface 16a of the second substrate mounting table 16 and the raw material gas ejection box 13, as shown in FIG. 9, as in the case of the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention.
When the electric field 25a is generated, as shown in FIG. 10, electric field concentration occurs due to the edge effect, and high-density plasma 22b is generated, in the same manner as in the case of the plasma CVD apparatus for diamond synthesis according to the first embodiment of the present invention.
When the substrate 11 is placed on the second substrate mounting table 16, if the material of the substrate 11 is a dielectric material, such as a silicon wafer or a diamond substrate, there is no change in the form of the electric field lines, and therefore, high-density plasma 22b shown in FIG. 10 is generated in the same manner as when the substrate 11 is not present.

Since the standing wave 25 generated in the region between the second substrate mounting table 16 and the raw material gas ejection box 13 has a cosine wave shape in the direction of the length L of the reaction vessel 7, the region in which uniform plasma is generated is a range of a diameter of approximately 0.25λ centered on the central axis 21a of the second substrate mounting table 16. Therefore, for example, when the power supply frequency is 2.45 GHz, the range of uniform plasma is 0.75×0.25×122 mm=22.8 mm, assuming that the wavelength shortening rate in the plasma is 0.75 and λ=122 mm.
For example, when the power supply frequency is 915 MHz, the range of the uniform plasma is 0.75×0.25×122 mm=61.1 mm, assuming that the wavelength shortening rate in the plasma is 0.75 and λ=326 mm.
For example, when the power supply frequency is 300 MHz, the range of the uniform plasma is 0.75×0.25×996 mm=186.7 mm, assuming that the wavelength shortening rate in the plasma is 0.75 and λ=996 mm.
Therefore, when the area of the substrate is large, the frequency of the supplied power is set low, for example, in the band of 300 MHz to 600 MHz, and when the area of the substrate is small, the frequency of the supplied power is set high, for example, to 915 MHz or 2.45 GHz, thereby enabling uniform diamond synthesis through the generation of uniform plasma.

Next, the operating procedure of the plasma CVD apparatus for synthesizing diamond according to the second embodiment of the present invention will be described with reference to Figures 9 and 10. Figure 8 will also be referred to.
First, the inside of the reaction vessel 7 is evacuated to a predetermined vacuum level through the exhaust ports 15a and 15b by a vacuum pump (not shown).
Next, the substrate 11 is carried in through the substrate carry-in/out passage opening 26a and the substrate carry-in/out valve 27, and placed on the second substrate placement table 16. The upstream side of the substrate carry-in/out valve 27 is connected to a load lock chamber (not shown) and is kept under vacuum.
Next, the surface of the substrate 11 is cleaned with hydrogen plasma, and the temperature of the substrate is set to, for example, 1,000° C. That is, only hydrogen gas is introduced as the raw material gas from a raw material gas supply source (not shown), and the pressure inside the reaction vessel 7 is set to, for example, 5 kPa. Then, for example, 1 kW is supplied from the second microwave power supply device 50 to the reaction vessel 7 through the antenna rod 51. At this time, the matching conditions for microwave propagation are adjusted by the isolator 50c attached to the coaxial tube 50b, the power monitor 50d (traveling wave, reflected wave), the matching device 5050e, and the plunger 9. The surface temperature of the substrate 11 is measured through the observation window 19 using a radiation thermometer (not shown), and when it reaches, for example, 1,000° C., the output of the second microwave power supply device 50 is temporarily reduced to zero. The substrate 11 and the second substrate support 16 are effectively heated by the magnetic heating effect (μ· ^H2 , where μ is magnetic permeability and H is magnetic field strength), the induction heating effect (σ· ^E2 , where σ is electrical conductivity and E is electric field strength) and the induction heating effect (σ· ^E2 , where σ is electrical conductivity and E is electric field strength).
Next, methane gas and hydrogen are selected as raw material gases from a raw material gas supply source (not shown). The gas supply conditions are, for example, a flow rate ratio of hydrogen flow rate/methane gas flow rate=100/1. Thereafter, methane gas and hydrogen gas, which are controlled to predetermined flow rates by mass flow controllers (not shown) for methane gas and hydrogen gas, respectively, from a methane gas source (not shown) and a hydrogen gas source (not shown), are ejected from the raw material gas supply hole 13c.
Next, an exhaust valve control device (not shown) attached to the exhaust ports 15a and 15b controls the opening and closing of the exhaust valve (not shown) to keep the internal pressure of the dome-shaped reaction vessel 7 at about 1 kPa to about 10 kPa. Here, for example, the pressure is set to 5 kPa and maintained.

Next, the output of the second microwave generator 50a is set to, for example, 500 W to 2 kW, for example, 1 kW here. At this time, matching conditions for microwave propagation are adjusted using an isolator 50c (not shown) attached to the coaxial tube 50b, a power monitor 50d (forward wave, reflected wave), a matching box 50e, and a plunger 9. The surface temperature of the substrate 11 is measured through an observation window 19 using a radiation thermometer (not shown), and it is confirmed that the surface temperature is, for example, 1,000° C.
Then, as shown in Fig. 9, plasma 22 of the raw material gas is generated in an area 23 (plasma generation area 23) between the second substrate mounting table 16 and the raw material gas introduction means 13. The plasma 22 is accompanied by high-density plasma 22b shown in Fig. 10, so the raw material gas can be effectively decomposed. When the raw material gas methane ( _CH4 ) and hydrogen ( _H2 ) are plasmatized by the high-density plasma 22b, _CH4 and _H2 are dissociated, generating high-concentration _CH3 radicals and atomic H, which are precursors for diamond formation. The _CH3 radicals and atomic H diffuse to reach the surface of the substrate 11.
That is, as shown in Fig. 8, the high concentration of _CH3 radicals and atomic H etc. generated in the plasma generation region 23 move to the surface of the substrate 11 by the diffusion phenomenon. A part of them is chemically adsorbed on the surface of the substrate 11. A part of the _CH3 radicals etc. chemically adsorbed on the substrate surface bonds in the form of C-C by a surface chemical reaction. The atomic H extracts H components and weakly bonded carbon components on the film surface and in the film. The extracted C and H components become gas and are discharged. On the substrate, C-C bonds are formed in a regular tetrahedral structure and diamond grows.

Next, since the thickness of the diamond to be formed is proportional to the duration of the generation of the plasma 22, the output of the second microwave power supply device 50 is set to zero when a predetermined time has elapsed since the start of the output supply from the second microwave power supply device 50. The diamond synthesis time is determined based on previously acquired data. Here, for example, it is set to 30 to 60 minutes, for example, 60 minutes.
The diamond synthesis time is determined based on data relating to the diamond synthesis rate, such as the dimensions of the reaction vessel 7, the distance d between the second substrate mounting stage 16 and the source gas introduction means 13, the substrate temperature, the flow rate of methane gas, the flow rate of hydrogen gas, pressure, microwave power, etc., which are obtained in advance.
After the synthesis of the desired diamond is completed, the supply of the methane gas and hydrogen gas is stopped, and the inside of the reaction vessel 7 is temporarily evacuated to a high degree of vacuum.
Thereafter, the substrate 11 is carried out from the substrate carry-in/out passage opening 26a through the substrate carry-in/out passage 26 and the substrate carry-in/out valve 27. After the substrate 11 is carried out, a new substrate 11 is carried in. Then, diamond is formed in the same manner as described above.

As explained above, in the plasma CVD apparatus for diamond synthesis according to the second embodiment of the present invention, a plurality of grooves 16b are formed on the main surface 16a of the second substrate mounting table 16 disposed in the reaction vessel 7, which contacts the substrate 11, and high-density plasma 22b can be generated near the main surface 16a due to the electric field concentration effect of the edges of the plurality of grooves 16b. Since the range of uniform plasma in the plasma generation region 23 depends on the electric field distribution of the standing wave generated inside the reaction vessel 7, it is possible to increase the area by selecting the frequency of the power generated by the second microwave power supply unit 50.
For example, when the power supply frequency is 2.45 GHz, the range of the uniform plasma is 0.75×0.25λ=22.8 mm, assuming that the wavelength shortening rate in the plasma is 0.75 and λ=122 mm.
For example, when the power supply frequency is 915 MHz, the range of the uniform plasma is 0.75×0.25λ=61.1 mm, assuming that the wavelength shortening rate in the plasma is 0.75 and λ=326 mm.
For example, when the power supply frequency is 300 MHz, the uniform plasma has a wavelength shortening rate of 0.75 and a wavelength shortening rate of λ=996 mm, and the length is 0.75×0.25λ=186.7 mm.
Therefore, when the area of the substrate is large, the frequency of the power supply is set low, for example, in the band of 300 MHz to 600 MHz, and when the area of the substrate is small, the frequency of the power supply is set high, for example, to 915 MHz or 2.45 GHz, thereby enabling high-speed, large-area, and high-quality diamond growth. In addition, the structure of the reaction vessel is simple, and the reaction vessel is easy to manufacture, resulting in an effect of reducing the manufacturing cost.

Third Embodiment
A plasma CVD apparatus for diamond synthesis according to the third embodiment of the present invention will be described with reference to Fig. 11. Fig. 11 is a cross-sectional view showing the configuration of a third substrate placement table, which is a component of the plasma CVD apparatus for diamond synthesis according to the third embodiment of the present invention.
The plasma CVD apparatus for diamond synthesis according to the third embodiment of the present invention is characterized in that it uses a third substrate mounting table 17 described below instead of the first and second substrate mounting tables 12, 16 which are components of the plasma CVD apparatus for diamond synthesis according to the first and second embodiments of the present invention.
11, reference numeral 17 denotes a third substrate mounting table. Reference numeral 17a denotes a main surface of the third substrate mounting table 17. The main surface 17a of the third substrate mounting table 17 is provided with a protrusion 17b having a triangular cross-sectional shape. The triangular protrusion 17b is formed of circular peaks and valleys concentric with the central axis 21b of the third substrate mounting table 17. Reference numeral 17c denotes a frame for ensuring stability in holding the substrate.
The dimensions of the triangular protrusion 17b are such that the distance between the circular peak and valley concentric with the central axis 21b of the third substrate supporting platform 17 is, for example, 1 mm to 10 mm, for example, 5 mm, and the height difference between the peak and the valley is, for example, 1 mm to 10 mm, for example, 5 mm.
When an electric field is generated in the normal direction of the main surface 17a of the third substrate mounting table 17, the protrusions 17b generate high-density plasma 22c due to electric field concentration. When high-density plasma 22c is generated, plasma decomposition of the source gas occurs effectively, enabling high-speed deposition of diamond synthesis.
The electric field distribution generated in the normal direction to the main surface 17a of the third substrate mounting table 17 depends on the standing wave of microwaves formed in the reaction vessel 7, as in the case of the plasma CVD apparatus for diamond synthesis according to the first and second embodiments of the present invention.
Therefore, similarly to the plasma CVD apparatus for diamond synthesis according to the first and second embodiments of the present invention, when the area of the substrate is large, the frequency of the power supply is set low, for example, in the band of 300MHz to 600MHz, and when the area of the substrate is small, the frequency of the power supply is set high, for example, to 915MHz or 2.45GHz, thereby enabling high-speed, large-area, and high-quality diamond growth. In addition, the structure of the reaction vessel is simple, and the reaction vessel is easy to manufacture, resulting in the effect of reducing the manufacturing cost.

Fourth Embodiment
A plasma CVD apparatus for diamond synthesis according to a fourth embodiment of the present invention will be described with reference to Fig. 12. Fig. 12 is a cross-sectional view showing the configuration of a fourth substrate placement table, which is a component of the plasma CVD apparatus for diamond synthesis according to the third embodiment of the present invention.
The plasma CVD apparatus for diamond synthesis according to the fourth embodiment of the present invention is characterized in that it uses a fourth substrate mounting table 18 described below instead of the first and second substrate mounting tables 12, 16 which are components of the plasma CVD apparatus for diamond synthesis according to the first and second embodiments of the present invention.
12, reference numeral 18 denotes a fourth substrate mounting table. Reference numeral 18a denotes a main surface of the fourth substrate mounting table 18. The main surface 18a of the fourth substrate mounting table 18 includes a protrusion 18b having a sine wave-shaped cross section. The sine wave-shaped protrusion 18b is formed of circular peaks and valleys concentric with the central axis 21c of the fourth substrate mounting table 18. Reference numeral 18c denotes a frame for ensuring stability in holding the substrate.
The dimensions of the sinusoidal protrusion 18b are such that the distance between the circular peaks and valleys concentric with the central axis 21c of the fourth substrate mounting platform 18 is, for example, 1 mm to 10 mm, for example, 5 mm, and the height difference between the peaks and the valleys is, for example, 1 mm to 10 mm, for example, 5 mm.
When an electric field is generated in the normal direction of the main surface 18a of the fourth substrate mounting table 18, the protrusions 18b generate high-density plasma 22d by generating electric field concentration. When high-density plasma 22d is generated, plasma decomposition of the source gas occurs effectively, enabling high-speed deposition of diamond synthesis.
The electric field distribution generated in the normal direction to the main surface 18a of the fourth substrate mounting table 17 depends on the standing wave of microwaves formed in the reaction vessel 7, as in the case of the plasma CVD apparatus for diamond synthesis according to the first and second embodiments of the present invention.
Therefore, similarly to the plasma CVD apparatus for diamond synthesis according to the first and second embodiments of the present invention, when the area of the substrate is large, the frequency of the power supply is set low, for example, in the band of 300MHz to 600MHz, and when the area of the substrate is small, the frequency of the power supply is set high, for example, to 915MHz or 2.45GHz, thereby enabling high-speed, large-area, and high-quality diamond growth. In addition, the structure of the reaction vessel is simple, and the reaction vessel is easy to manufacture, resulting in the effect of reducing the manufacturing cost.

1...first microwave power supply device;
2...waveguide,
5...Dielectric window (quartz window),
7... reaction vessel,
9...plunger,
11...Substrate,
12: First substrate mounting table,
12a...Main surface of the first substrate mounting table,
12b...hole,
12bf: electric field concentration region,
13... raw material gas ejection box,
13c...raw material gas ejection hole,
15a, 15b...exhaust port,
16: Second substrate mounting table,
16a: Main surface of the second substrate mounting table;
16b...groove,
17: third substrate mounting table,
17a: Main surface of the third substrate mounting table;
17b: triangular protrusion,
18...fourth substrate mounting table,
18a: Main surface of the fourth substrate mounting table;
18b: sinusoidal projection;
19...observation window,
22...Plasma,
22a, 22b, 22c, 22d...high density plasma,
25...standing waves,
25a...electric field,
50: second microwave power supply;
51...Antenna rod.

Claims (5)

A plasma CVD apparatus for diamond synthesis, comprising: a reaction vessel having a source gas introduction means for introducing a source gas, an exhaust means, and a substrate placement stage on which a substrate is placed; and a microwave power supply device for supplying microwaves to the reaction vessel through a dielectric window or an antenna rod, the source gas introduced from the source gas introduction means being converted into plasma by the microwaves supplied from the microwave power supply device, to form diamond on a surface of the substrate placed on the substrate placement stage,
The substrate supporting table has a main surface in contact with the substrate, the main surface is arranged parallel to a plane perpendicular to the electric field direction of the microwaves supplied from the microwave power supply device, and a plurality of grooves, a plurality of holes, or a plurality of protrusions are formed on the main surface. The plasma CVD apparatus for diamond synthesis according to claim 1, characterized in that the grooves on the main surface of the substrate mounting table have a rectangular cross-sectional shape and are arranged concentrically with the central axis of the substrate mounting table. The plasma CVD apparatus for diamond synthesis according to claim 1, characterized in that the holes in the main surface of the substrate table have a rectangular cross-sectional shape, and the centers of the adjacent holes are arranged at approximately equal intervals. The plasma CVD apparatus for diamond synthesis according to claim 1, characterized in that the multiple protrusions on the main surface of the substrate mounting table have a triangular or sinusoidal cross-sectional shape and are arranged concentrically with the central axis of the substrate mounting table. A plasma CVD apparatus for diamond synthesis according to any one of claims 1 to 4, characterized in that the microwave power supply generates microwave power at a frequency selected from the range of 300 MHz to 3 GHz.

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